(d,l)2-Mercaptomethyl-5-guanidinopentanoic acid is reported as a potent inhibitor of carboxypeptidase B [Ondetti, M. A., Condon, M. E., Reid, J., Sabo, E. F., Cheung, H. S., and Cushman, D. W., Biochemistry 18, 1427-1430 (1979)]. More recently, this compound has been shown to have excellent activity in inhibiting serum carboxypeptidase N (SCPN) [Hugli, T. E., Gerard, C., Kawahara, M., Scheetz, M. E., Barton, R., Briggs, S., Koppel, G., and Russell, S., Molecular and Cellular Biochemistry 41, 59-66 (1981)].
Ondetti et al, supra, details a multi-step sequence for the preparation of (d,l)2-mercaptomethyl-5-guanidinopentanoic acid. It is to a modification of the described method of preparation that this invention is directed. In the sequence described by Ondetti et al., supra, an intermediate, 2-acetylthiomethyl-5-aminopentanoic acid, is prepared. The trifluoroacetate salt of this material, as described in the Ondetti et al. reference, obtained as a pale yellow impure oil, is converted to the above intermediate by a cumbersome chromatographic procedure employing AG50WX2, a cation exchange resin. It has been discovered that this conversion and product recovery can be accomplished by a simple and rapid method using a base and a polar solvent.